Blood thinners fall into two categories: antiplatelet drugs and anticoagulants. Antiplatelets keep blood cells from sticking together; examples are aspirin and clopidogrel, sold under the brand name Plavix. Anticoagulants keep proteins in the blood from forming clots; an example is warfarin, sold under the brand names Coumadin, Dicumarol or Miradon. Consuming certain foods and beverages can inhibit or increase the blood-thinning properties of these drugs.
Foods Containing Vitamin K
The liver needs vitamin K to produce blood-clotting proteins. When taking warfarin, the National Institutes of Health says it's important to be consistent with intake of foods containing vitamin K so the doctor can calculate your dosage correctly. Consuming less than when your dosage was calculated increases the risk of bleeding; consuming more increases the risk of clotting. Foods containing moderate to high amounts of vitamin K include kale, spinach, turnip greens, collards, Swiss chard, mustard greens, Brussels sprouts, green leaf lettuce, endive, romaine, broccoli, parsley, beef liver and chicken liver. In some cases, cooking can increase the amount of vitamin K available to the body from these foods. Iceberg lettuce, red cabbage, asparagus and soybean oil also contain vitamin K, but in smaller amounts.
Green Tea, Cranberry Juice and Alcohol
Some beverages can affect the action of anticoagulants. Green tea, for example, is high in vitamin K. If you increase your consumption after your warfarin dosage is calculated, your risk of clotting is increased. If you decrease your consumption, your risk of bleeding is increased. Cranberry juice and alcohol increase the anticoagulant effect of warfarin and can lead to bleeding problems. Discuss with your doctor whether you can consume these beverages or whether you should avoid them completely.
Foods Containing Omega-3 Fatty Acids
Omega-3 fatty acids can reduce inflammation in the body and are good for heart health. They are found in fatty, cold-water fish such as salmon, mackerel, sardines and halibut, and can be taken in the form of fish-oil supplements. They are also in flaxseeds, pumpkin seeds, soybeans, walnuts, krill, algae, canola oil and oils made from flaxseed, soybeans, pumpkin seeds, purslane, perilla seeds and walnuts. However, omega-3 fatty acids increase the risk of bleeding. Discuss omega-3 supplementation and diet with your doctor if you are on any blood-thinning drugs, including aspirin or warfarin.
Many herbs used as supplements or as flavorings in food can increase or decrease the action of blood-thinning drugs. The NIH lists several, including arnica, bilberry, butchers broom, cat's claw, dong quai, feverfew, forskolin, garlic, ginger, ginkgo, horse chestnut, insositol hexaphosphate, licorice, melilot or sweet clover, pau d'arco, red clover, St. John's wort, sweet woodruff, turmeric, willow bark and wheat grass. Before taking any of these herbs, discuss their use with your doctor to see if they will increase or decrease the action of your blood-thinner.